1. Field of the Invention
This invention relates to the design and construction of a loudspeaker, particularly to the design and construction of a horn type loudspeaker.
2. Prior Art
The structure of a conventional horn type loudspeaker, as shown in FIG. 1, usually consists of a drive unit 1 and a horn member 2. The drive unit 1 includes: an outer shell 10; a yoke 11 with a center pole 110 vertically protruding from its center portion; a hollow permanent magnet 12 and a guide ring 13 made of a kind of material with magnetic conductivity, said magnet 12 and guide ring 13 stacking sequentially around said center pole 110 to form gaps 120, 130 therebetween; a damper 14 formed with a dome-shaped diaphragm 15 at its central hollow portion and affixed to the guide ring 13 around its edge by a fixing plate 16 on top and a gasket 141 underneath made of an insulating material; and a voice coil 17 attached to the bottom outer surface of the diaphragm 15 extending downward into gap 130, and connected electrically to a D.C. electrical power source(not shown). The fixing plate 16 has a hole 160 at its center portion corresponding to the position of the diaphragm 15, and an air chamber 18 is formed between the fixing plate 16 and the diaphragm 15 with its adjoining damper 14.
The horn members 2 usually comprise: a horn 21 with its lower end combining with the outer shell 10 of the drive unit 1; a throttle 23 force-fitted vertically into the hole 160 of said fixing plate 16; and a reflection cover 22 between the horn 21 and the throttle 23 with a tip 221 on its inner bottom surface pointing inwardly towards the central portion of the said throttle 23.
The poles of the center pole 110 and the guide ring 13 are located such that the flux will radiate from the center pole 110 towards the guide ring 13. The voice coil 17 will be energized by the input of voice through a microphone, and the appropriate electrical power source. The directions of the current in the voice coil 17 and said flux are crossed with each other thereby actuating the diaphragm 15 to move back and forth axially, driving the air in the air chamber 18 to form corresponding sound waves. Said sound waves will radiate through the throttle 23, are reflected by the reflection cover 22, travel upward through the horn 21 and are eventually discharged from the open end.
It is to be understood that the dimensions of the horn 21 of the conventional horn type loudspeaker is supposed to follow the standard scale shown in FIG. 2. According to this standard, the minimum size and weight of a 100 decibel (dB) horn type loudspeaker are 90 mm (diameter).times.95 mm (height) and 440 grams respectively. It is quite impossible for the conventional horn type loudspeaker to have a size and weight small and light enough for miniature applications such as for pocket-size security alarms.